A:Answer All of the above. The RAM can be upgraded to 32GB, you could swap out the SSD for any sized one you wanted and the hard drive could be swapped out for a 2TD (5200rpm though) or any 2.5" SSD. I've also seen kits to swap out the DVD drive for an SSD as well. You can also get external SSD or HDD set-ups , including hot swap ( I have one), because the USB is plenty fast. As it sits it's pretty well set up.
Hope that helps,